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ETHYL BROMIDE                                57

through a funnel, the stem of which is drawn out so as to pass
through the narrow neck. The bottle is placed in a mixture of *
snow or pounded ice and left a quarter to half an
hour, until the contents have a temperature of o.
The meniscus is now adjusted until it coincides
with the mark on the neck of the bottle. If
more liquid has to be added, this may be
done from a small pipette with capillary de-                     ^

livery tube ; if some of the  liquid has to be                     I  ,*'

removed, a thin   roll  of filter  paper   may be                     \   f

inserted   which will absorb it.    The   bottle  is
then stoppered,dried on the outside, left in the                    . l|*

balance case  for  a  quarter of an  hour,  and                    J

weighed.    It   is   then   emptied,   cleaned,  and                     ' (   |

dried, and filled with distilled water previously                       i

boiled.    The water is cooled to o, the meniscus                     <' V

adjusted   and   the   bottle   weighed, the   same
IG 45'        process being repeated as that just described.                        -*

The following expression will  give the specific gravity of the                     .    '

liquid at o compared with water at o :                                                       . jf

Where iu  weight of empty bottle,
w.2 =                 bottle,and water at o,
7e/3 =                 bottle and liquid at o;
or, if compared with water at 4, the above number must be
multiplied by the density at o = 0*999873.
A very delicate and useful piece of apparatus, which is
readily made with the blow-pipe, is Perkins5 modification of
Sprengel's pyknometer.1 It is especially adapted for small quan-
tities of liquid and for the more volatile ones. The apparatus
(Fig. 46) consists of a U~tuDe to hold from 2 to 10 c.c., drawn
out at each end into a fine capillary. The one capillary limb, #, is
bent outwards and is furnished with a small bulb ; the other, ,
is bent at a right angle with the first. On the limb <z, between
the bulb and the top of the U-tube a mark is etched. The
1 Trans. Chem. Soc. 1884, 45, 421.